Synchronized Operation of DSP-Based Generalized Impedance Controller With Variable-Speed Isolated SEIG for Novel Voltage and Frequency Control

In this paper, the performance of a novel two-loop control strategy for a three-phase self-excited induction generator (SEIG), used in wind/microhydro/biogas-based isolated generation schemes, is presented. The implementation of the grid-interactive synchronization of the generalized impedance controller (GIC), an impedance-controlled operation of pulse width modulation (PWM) voltage-source converter, with SEIG is described. The SEIG frequency is tracked using digital phase-locked loop implemented on a dSpace DSP platform. The open-loop SEIG-GIC system is experimentally analyzed for the sensitivity of the SEIG voltage and frequency to GIC modulation index m and phase angle δ. Based on this, a simple and practical control strategy with proportional-integral (PI)-based voltage and frequency feedback loops is evolved for the regulation of the SEIG voltage and frequency. A novel design procedure for both the PI controllers for stable closed-loop operation is presented. The performance of the proposed closed-loop system is experimentally tested under speed and load perturbations.